Field of the Invention
The present invention relates to a liquid ejection head that ejects liquid.
Description of the Related Art
Liquid ejection apparatuses that eject liquid such as ink to record images on a recording medium are generally equipped with a liquid ejection head that ejects liquid. Known examples of a mechanism for ejecting liquid from the liquid ejection head include a mechanism that uses a pressure chamber whose capacity can be varied with an piezoelectric element and a mechanism that uses a heating element that heats liquid to generate bubbles, thereby generating pressure. The pressure generated using these mechanisms causes the liquid in the pressure chamber to be ejected through ejection ports at an end of the pressure chamber. The pressure chamber is under a minute negative pressure. The negative pressure and the capillary action of the ejection ports are balanced to hold the interface of the liquid in the ejection ports.
It is known that the presence of bubbles in the pressure chamber significantly reduces the droplet ejection performance of liquid ejection heads. The bubbles in the pressure chamber are generated because of various factors including cavitation caused due to a pressure change during ejection and bubbles coming from a liquid supply channel. The bubbles in the pressure chamber are generally discharged using suction recovery, that is, by stopping printing, applying negative pressure to the ejection ports, with the ejection ports capped, and sucking the bubbles together with the liquid. However, the suction recovery, which needs to stop printing, reduces the production efficiency and wastes a large quantity of liquid. This is disadvantageous for commercial liquid ejection apparatuses that output high-quality images at a high speed in terms of time and cost.
PCT Japanese Translation Patent Publication No. 2012-532772 discloses a liquid ejection apparatus equipped with inflow channels and outflow channels in pressure chambers. Liquid is supplied to the pressure chambers through the inflow channels, part of which is ejected through ejection ports communicating with the pressure chambers, and the remaining liquid is discharged to the outflow channels. The discharging of the liquid to the outflow channels allows the liquid to be circulated, thus allowing bubbles and dust to be removed without stopping printing. This can also prevent the liquid from increasing in viscosity due to evaporation through the ejection ports. The pressure chambers, the inflow channels, and the outflow channels are provided for the individual ejection ports. The inflow channels communicate with a common liquid channel provided in common to each ejection port train. The outflow channels communicate with another common liquid channel provided in common to each ejection port train.
Liquid ejection heads designed to achieve high-resolution output are provided with ejection ports at high density. Therefore, in the liquid ejection apparatus disclosed in PCT Japanese Translation Patent Publication No. 2012-532772, the common liquid channel provided in common to each ejection port train is narrow and long. This causes a non-uniform pressure distribution in the common liquid channel due to channel resistance, exerting different negative pressures on the different pressure chambers, which may cause variations in ejection performance. Since the channel resistance depends on the viscosity of the liquid, larger variations in ejection performance can occur in printing with high-viscosity liquid, such as UV ink and solder paste, causing degradation of image quality.